ON NERVE-EXCITATION BY THE NERVE-CURRENT. 139 



Closure tetanus of the nerve by the agency of its own current. 



The great liability of cooled frogs to tetanic excitation explains 

 the fact that even the derivation or short circuiting of the nerve- 

 current is sufficient in suitable preparations to cause a closure tetanus 

 which in favourable cases may be lasting, and of such steadi- 

 ness and energy as to be comparable to the tetanus produced 

 by induction currents. In most cases, it is true, the tetanus is 

 unsteady or clonic, and the derivation of the nerve-current often 

 brings about only an irregular agitation of the muscles ; in short, 

 there are here manifested all those appearances which one may 

 observe when the closure of a weak battery-current sent through 

 the nerve causes an enduring excitation of the nerve, and not 

 merely closure contractions. 



Whichever of the above described methods of establishing de- 

 rivation be used, there will always result in certain cases, with 

 very excitable preparations, an enduring excitation of the nerve, 

 sometimes after the first closure only, sometimes after repeated 

 ones. This lasting excitation may show itself by weak, irregular, 

 or even rhythmical movements of single parts, or by stronger clonic 

 spasms, or finally by well marked stretching tetanus. If to the 

 original tendency towards tetanic excitation there be added any 

 drying of the nerve, a permanent closure tetanus appears all the 

 more readily. If the preparation is capable of responding to deriva- 

 tion of its nerve-current by a lasting excitation, it is no longer so 

 necessary to provide for the rapid closure of the derivation-circuit, 

 because, even failing a closure contraction, the persistent excitation 

 is still appreciable. 



An observation belonging here is as follows : I allowed the 

 end of a dependent nerve of a galvanoscopic frog's limb to dip 

 into salt-solution O'6 / . I then made above the level of the 

 fluid, a kind of transverse section by crushing the nerve with fine 

 forceps. I allowed the contractions caused by this proceeding 

 to subside, and when the preparation had become quite quiescent, 

 I gradually raised the vessel containing the salt-solution so that 

 the nerve was immersed in it deeper and deeper. As soon as the 

 surface of the fluid rose above the crushed part a tetanus of the 

 preparation appeared, which became stronger as I continued to 

 raise the vessel, and reached its maximum when the surface of the 

 fluid was about I cm. above the crushed part. If I raised the 

 vessel still higher, the tetanus diminished, without, however, entirely 



